Light-emitting devices using light-emitting diode (LED) elements are being widely used. An old-type light-emitting device has a structure shown in FIG. 3. More specifically, an LED element 33 is bonded to a substrate 31 with a die-bonding adhesive 32, and a p electrode 34 and an n electrode 35 on the upper surface of the LED element 33 are wire-bonded to connection terminals 36 of the substrate 31 with gold wires 37. The entire LED element 33 is sealed with a transparent molding resin 38. However, in the light-emitting device shown in FIG. 3, light having a wavelength of 400 to 500 nm and emitted upward from the LED element 33 is absorbed by the gold wires, and part of the light emitted downward is absorbed by the die-bonding adhesive 32. Therefore, there is a problem in that the light emission efficiency of the LED element 33 is reduced.
For this reason, as shown in FIG. 4, flip-chip mounting of the LED element 33 has been proposed (Patent Literature 1). In this flip-chip mounting technique, bumps 39 are formed on the p electrode 34 and the n electrode 35, respectively, and a light reflecting layer 40 is provided on a bump-forming face of the LED element 33 so that the light reflecting layer 40 is insulated from the p electrode 34 and the n electrode 35. The LED element 33 and the substrate 31 are connected and fixed to each other by curing an anisotropic conductive paste 41 or an anisotropic conductive film (not shown). Therefore, in the light-emitting device in FIG. 4, the light emitted upward from the LED element 33 is not absorbed by the gold wire and almost all the light emitted downward is reflected by the light reflecting layer 40 and is then emitted upward. Thus, the light-emitting efficiency (light extraction efficiency) is not reduced.
As a binder resin mixed in an anisotropic conductive paste or an anisotropic conductive film for anisotropic conductive connection of LED to a substrate, an epoxy resin having relatively favorable heat resistance, light stability, and connection reliability has been widely used (Patent Literature 2). However, the epoxy resin can absorb light from the near ultraviolet wavelength region to the near infrared wavelength region due to the molecular structure as shown in FIG. 5A. Further, if heat or light (for example, successive UV irradiation at 120° C.) is applied over a long term, cleavage of a molecular chain or oxidation occurs, and a light transmittance spectrum largely varies as shown in the arrow in FIG. 5B. Therefore, there has been a problem in which the light reflectance and the total luminous flux of LED are significantly reduced due to the long-term use of the light-emitting device. This tendency becomes more remarkable as the power of an LED element is increased and the wavelength thereof is shortened in recent years.
For this reason, a silicone resin having few such defects is attempted to be used in recent years.